The invention relates to an emptying device for a bulk silo with a flat or slightly inclined silo bottom, outer slope and open air driven conveying chutes distributed over the silo bottom which run to a ventilated annular chamber located inside the outer slope of the silo bottom, the bottom of which annular chamber is provided with open air driven conveying chutes and is inclined toward the discharge opening.
Such a known emptying device (DE-PS No. 23 36 984) can be used very effectively to empty in particular large-diameter silos, whereby the basic concept of the known ventilated emptying and pressure-release chamber is employed. This device avoids in particular the depositing of considerable amounts of the bulk material in the vicinity of the silo wall which gradually solidify and can no longer be removed. The mentioned DE-PS No. 23 36 984 is incorporated herein by reference in its entirety.
In order that the ventilating processes in the silo bottom and in the annular chamber do not have an adverse effect on each other, the corresponding air driven conveying chutes must have a certain distance from each other. For this reason, the essentially radially extending air driven conveying chutes of the silo bottom do not quite extend to the essentially circumferential air driven conveying chutes of the annular chamber. Cones or walls of material can form in the intermediary area which can hinder the effective operation, especially in the case of material which is not very stable in storage and solidifies very rapidly. Such materials which are not very stable in storage and solidify readily are e.g. flue dust with its properties which vary according to the type of coal and the firing conditions.
The invention has the object of creating an emptying device which can be used with good effect for bulk materials which are not very stable in storage.
The invention solves this object by making the bottom of the annular chamber lower than the silo bottom.
Having a lower position does not mean in this instance that parts of the annular chamber bottom are lower, as is also the case in the previously known devices, namely, in the vicinity of the discharge opening. Rather, the entire annular conduit is intentionally placed lower so that the ventilated bottoms of the silo and of the annular chamber are distinctly displaced from each other. The bottom of the annular chamber should be at least 50 cm lower than the silo bottom. It has proven to be especially advantageous if the bottom of the annular conduit is 1 to 5 m lower. Again, it is particularly advantageous if the bottom is 2 to 3 m lower than the silo bottom.
Due to the separation in height between silo bottom and annular chamber bottom, the air driven conveying chutes of the silo bottom can be run right into the annular chamber. Thus, no unventilated areas remains here in which said materials, walls or cones can form and gradually solidify.
The emptying device operate so effectively that it is even possible to use smaller values for the slope angle than in the past. While the slope angle of the outer slope was previously approximately 60.degree. to 70.degree., this slope angle can now be 50.degree. to 55.degree. relative to the horizontal. Since the material slides less readily over such a less steep slope, it is effectively braked here, which aids in even emptying and prevents too much material from passing at the same time into the annular conduit.
This lesser slope angle has the essential advantage that when the slope is made of concrete, no double shell is necessary any longer, that is, a shell which covers the area for the concrete above and below, but rather only one single shell upon which the concrete is applied during construction. The concrete can not slip off on account of the lesser slope angle and need only be subjected to a smoothing surface treatment after it hardens.
It is advantageous if the air driven conveying chutes of the silo bottom extend into the annular chamber so that the material does not fall down at the edge of the annular chamber but rather more towards the center so that it can not back up on the edge and possibly form more downs.
It is also possible in accordance with the invention as a result of the vertical spatial displacement of silo bottom and annular chamber bottom to load the air driven conveying chutes of the annular chamber with a lesser air pressure than the air driven conveying chutes of the silo bottom. This entails the following advantage.
A relatively greater air pressure must always be used for the silo bottom so that the material can be effectively fluidized. If an equally great air pressure is not selected for the annular chamber but rather a lower air pressure, then the discharge speeds of the material from the discharge opening or the discharge openings are also decreased so that the wear on the discharge slides or dosing devices is diminished. Foreign bodies and developing granulates are primarily responsible for this wear which can not do as much damage at the lower discharge speeds. The danger of clogging also drops, since the openings no longer have to be as small as was previously necessary for a careful discharging of the exiting material.
The invention also achieves the surprising advantage that the intensive circular flow within the annular chamber to the discharge opening occurs independently of the radial flows of the silo bottom. It is possible thereby, as is known, for particular cyclically different areas of the air driven conveying chutes of the silo bottom to be loaded with compressed air so that the material can not solidify anywhere.